Preparation Of Mg/Al-LDH Modified Biochar And Its Removal Of Cd²⁺ And Pb²⁺ From Aqueous Solution

Heavy metal pollution caused by human production and life is becoming increasingly serious and has developed into a global problem.As heavy metal pollution has seriously harmed farmland and crops,it has caused great losses to human life and economy.Currently,many researches are devoted to find methods that can remediate heavy metal pollution,however,traditional adsorbents have been difficult to meet these needs.Therefore,there is an increasing interest in developing new adsorbents and applying them to heavy metal contamination.In this study,biochar was prepared from maize straw as biomass raw material,and the maize straw-based biochar was optimized by preparing Mg/Al layered bimetallic hydroxide with EDTA intercalation by co-precipitation method to prepare Mg/Al layered bimetallic hydroxide modified biochar（Mg/Al-LDH BC）and used for the removal of heavy metals Cd²⁺and Pb²⁺from aqueous solution.In this study,Mg/Al layered bimetallic hydroxide modified biochar materials were firstly prepared,and the physicochemical properties of Mg/Al layered bimetallic hydroxide modified biochar were determined by scanning electron microscopy（SEM）,Fourier infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）and other characterization methods.The effects of different conditions on the adsorption of Cd²⁺and Pb²⁺in water by Mg/Al-LDH modified biochar were investigated by varying the initial p H of the aqueous solution,the material dosage,the adsorption reaction time,the initial concentration of the solution,and the reaction temperature,and the kinetic model,isotherm model and thermodynamic fitting were carried out respectively.LDH modified biochar was studied for the simultaneous removal of Cd and Pb from water,and the kinetic model and isotherm model were fitted by varying the adsorption reaction time and the initial concentrations of Cd and Pb to analyze the competitive adsorption law;finally,the mechanism of Cd and Pb adsorption by Mg/Al-LDH modified biochar was investigated by Fourier infrared spectroscopy and X-ray diffraction analysis of the modified materials after the adsorption of Cd and Pb,and the main results are as follows:（1）The Mg/Al-LDH BC materiall was successfully fabricated and the characterization results by SEM,FTIR,XPS and XRD showed that the EDTA intercalated Mg/Al-LDH was successfully loaded onto the biochar.The Mg/Al-LDH modified biochar has a large specific surface area and rich pore structure with abundant surface functional groups,such as-OH,C=C,C=O,-COOH,Mg-O,Al-O,etc.（2）The adsorption equilibrium time of Cd²⁺adsorption in water by Mg/Al-LDH modified biochar was 240 min,and the equilibrium adsorption amount was 98.34 mg/g.The adsorption kinetics was in accordance with the quasi-secondary kinetic model fitting,so the adsorption process belonged to chemisorption,and the isothermal adsorption data was in accordance with the Langmuir model fitting,which belonged to monomolecular layer adsorption.（3）The adsorption equilibrium time of Pb²⁺adsorption in water by Mg/Al-LDH modified biochar was 240 min,the balance sorption amount was 93.59 mg/g,the optimized material dosage was 0.4 g/L,the optimal p H of the solution was 5.0,and the adsorption procedure was in conformity with the quasi-secondary kinetic model fitting with the Langmuir model,which belonged to single layer chemical adsorption.（4）The results of the binary simultaneous removal system showed that the simultaneous adsorption of Cd²⁺and Pb²⁺by Mg/Al-LDH modified biochar had a certain competitive relationship,and the adsorption of Mg/Al-LDH modified biochar under the coexistence of Cd²⁺and Pb²⁺was in accordance with the quasi-secondary kinetic model fitting,and the main mechanisms of Cd²⁺and Pb²⁺removal by Mg/Al-LDH modified biochar were electrostatic attraction and carbonate precipitation by FTIR and XRD characterization of the modified materials after adsorption.